Combustion of coal is a potential source of toxic emissions to the atmosphere, including heavy metals. Combustion processes are considered the most important sources of heavy-metal pollutants to the atmosphere—particularly power generation, smelting, and incineration. It is important that emissions of potentially toxic air pollutants from coal combustion and biomass are measured and, if necessary, controlled in order to limit any deleterious environmental effects. Increasing concern about the effects of trace pollutants in the environment has led to the introduction of emission standards for some of these pollutants.
Coal, as the most abundant fossil fuel, accounts for ˜40% of the electricity produced throughout the world. Coal-fired power plants release to the environment SO2 and NOx, as well as CO2 and N2O, particulate matter, mercury (Hg) and other pollutants such as cadmium (Cd), arsenic (As), molybdenum (Mo), vanadium (V) and various acid gases. Average values for trace-metal contaminants in coal range from about 0.093 mg/kg for Cadmium to 47 mg/kg for Boron.
The US National Research Council (NRC) classified contaminants from coal based on adverse health effects and abundances in coal. As major concern, the NRC listed arsenic, boron, cadmium, lead, mercury, molybdenum and selenium, where arsenic, cadmium, lead and mercury are toxic to most biological systems. Additional concern was directed to chromium, vanadium, copper, zinc, nickel and fluorine.